When I was on a "limited budget" and did not really have a place to shoot. In fact I went for almost 6 months without firing a single round.
I took up archery. I shot in my back yard every day.
When I was able to get back to shooting I found that my scores had improved significantly.
I believe that Pulling the bow strengthened my shooting specific muscles and improved my concentration.
Another method I have used is meditation. I picture the target and mentally move through all of the steps in the shooting process. Bullseye shooters mentally shoot the round before they ever raise the pistol and fire.